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Biomedical subjects

B Das

Publications and source records attributed to B Das.

At least 19 recordsLinked to original sources
PubMed1995

Non-Newtonian flow of blood in an arteriosclerotic blood vessel with rigid permeable walls.

The steady, laminar and fully developed flow of blood in an arteriosclerotic blood vessel with rigid permeable walls is investigated, taking into account the slip condition at the vessel walls. The constitutive equation of blood is represented by a Casson fluid model. The model is used to study the influence of the yield stress on blood flow through arteriosclerotic arteries. The variation of the flow resistance and wall shear stress, with permeability parameter, slip parameter and Casson number are obtained for different sizes of growth of the arteriosclerotic lesions. Comparison of the results is made with available results that consider the impervious wall and those that consider blood as a Newtonian fluid. It is found that permeability has a significant effect on the values of flow resistance and wall shear stress. Biological implications of the present model on different arterial diseases are discussed.

Aged↗
PubMed1995

Computer-aided human modelling programs for workstation design.

In designing a workstation, computer-aided human modelling programs can be used advantageously to analyse human-fit to the workstation components. The analysis is performed within a three-dimensional computer graphics environment. To illustrate the current state of development, six representative programs were selected: CYBERMAN, COMBIMAN, CREW CHIEF, JACK, SAMMIE, and MANNEQUIN. The programs differ considerably in terms of system requirement, operating characteristics, applicability and the various ergonomic evaluation functions available in the human modelling programs. The comparative analysis of the programs will aid the user to select the appropriate program for a particular workstation design.

Anthropometry↗
PubMed1995

Studies on the genesis of Vibrio cholerae O139: identification of probable progenitor strains.

Four lines of evidence suggest that the recent outbreak strains of Vibrio cholerae O139 could have emerged from serogroup O1 strains typified by isolates M01 and M0477 described in this paper, which are neither truly classical nor truly E1 Tor in their biotype attributes. Firstly, like all O139 isolates, these O1 strains, isolated in Madras during and before the O139 outbreak, were resistant not only to polymyxin B but also to all biotype-specific choleraphages, i.e. classical phage phi 149 and E1 Tor phages e4 and e5. Secondly, the restriction fragment pattern (RFP) polymorphism displayed by these strains for the cholera toxin (ctx) gene, were identical with those produced by O139 isolates but were different from those of O1 type strains, namely V. cholerae 569B (classical) and V. cholerae MAK757 (E1 Tor). Thirdly, all the O139 isolates and the two O1 isolates carried an identical large number of copies of cholera toxin gene in their chromosomes. Finally, the outer-membrane protein profiles of strains M01 and M0477 were identical to those of O139 isolates but were different from those displayed by strains 569B and MAK757.

Bacterial Outer Membrane Proteins↗
PubMed1994

Cloning and analysis of human cDNAs encoding a 140-kDa brain guanine nucleotide-exchange factor, Cdc25GEF, which regulates the function of Ras.

Ras proteins bound to GDP are biologically inactive while those bound to GTP are active. Ras-specific guanine nucleotide-exchange factors (GEFs) have been shown to activate Ras proteins. We used oligodeoxyribonucleotide primers with sequences similar to the cDNAs of rat and mouse cdc25 (encoding a Ras-GEF) to amplify, by the PCR, sequences with the potential to encode a 1275-amino-acid protein homologous to the rodent Cdc25GEF proteins. Northern blot analysis detected a brain-specific 5-kb transcript. We provide evidence for a novel alternately spliced transcript of cdc25 and show that these alternately spliced transcripts are differentially expressed in various regions of the adult nervous system. Antibodies raised against the C terminus of the protein recognize a 140-kDa protein in brain extracts of human, rat, guinea pig and cow; the 140-kDa protein is associated predominantly, if not exclusively, with a crude membrane fraction of brain. The C terminus of human Cdc25GEF can complement the loss of CDC25 function in Saccharomyces cerevisiae. A glutathione S-transferase fusion protein containing the C terminus of the cdc25 product can stimulate guanine nucleotide exchange on H-Ras in vitro. Further, the Cdc25-fusion protein binds tightly to the nucleotide-free form of H-Ras in vitro, and this binding is reversed by the addition of GTP.

Alternative Splicing↗
PubMed1994

A novel ligand in lymphocyte-mediated cytotoxicity: expression of the beta subunit of H+ transporting ATP synthase on the surface of tumor cell lines.

Extracellular adenosine triphosphate (eATP) has been suggested to play a role in lymphocyte-induced tumor destruction. We now provide evidence that a protein responsible for ATP synthesis in mitochondria may also play a physiologic role in major histocompatibility complex-independent, lymphocyte-mediated cytotoxicity. A 51.5-kD protein (p51.5) bearing structural and immunologic characteristics of the beta subunit of H+ transporting ATP synthase (E.C. 3.6.1.34, beta-H+ATPase, published molecular mass of 51.6 kD) was detected on the plasma membrane of three different human tumor cell lines studied. NH2-terminal amino acid sequence analysis of purified p51.5 from K562 tumor cells revealed 100% homology of 16 residues identified in the first 21 positions to the known sequence of human mitochondrial beta-H+ ATPase. Antibody directed against a 21-mer peptide in the ATP binding region of beta-H+ ATPase (anti-beta) reacted with only one band on Western blots of whole tumor extracts and tumor membrane extracts suggesting that the antiserum reacts with a single species of protein. Anti-beta reacted with the cell membranes of tumor cells as determined by fluorescence-activated flow cytometry and immunoprecipitated a 51.5-kD protein from surface-labeled neoplastic cells (but not human erythrocytes and lymphocytes). Purified p51.5 bound to human lymphocytes and inhibited natural killer (NK) cell-mediated cytotoxicity. Furthermore, anti-beta treatment of the K562 and A549 tumor cell lines inhibited NK (by > 95%) and interleukin 2-activated killer (LAK) cell (by 75%) cytotoxicity, respectively. Soluble p51.5 upon binding to lymphocytes retained its reactivity to anti-beta suggesting that the ATP binding domain and the lymphocyte-receptor binding domain reside in distinct regions of the ligand. These results suggest that beta-H+ ATPase or a nearly identical molecule is an important ligand in the effector phase (rather than the recognition phase) of a cytolytic pathway used by naive NK and LAK cells.

Amino Acid Sequence↗
PubMed1994

Refolding of denatured lactate dehydrogenase by Escherichia coli ribosomes.

Escherichia coli ribosomes were used to refold denatured lactate dehydrogenase from porcine muscle. This activity of ribosomes, unlike most of the chaperons, did not require the presence of ATP. The molar concentration of ribosomes required for this refolding was comparable with that of the enzyme. Restoration of the enzyme activity was demonstrated using assays for both the forward and backward reactions. Binding of the denatured enzyme to ribosomes and its refolding were fairly rapid processes as revealed by the time course of the reaction and inhibition of folding when the denatured enzyme was allowed to refold spontaneously for short times before the addition of ribosomes. This protein-folding activity was detected in 70 S ribosomes as well as its RNA, in 50 S particles and in 23 S rRNA. However, 30 S particles failed to refold the enzyme.

Escherichia coli↗
PubMed1994

Infection in haematological malignancies.

Fifty-six febrile episodes in 30 haematological malignancy cases were evaluated. Of these episodes 60.7% were in leukaemia cases. Clinical evaluation and investigation suggested infection in 42 episodes (75%) of fever and in rest 14 (25%) no identifiable cause could be found. Bacterial infection predominated with an incidence of 80.9% followed by fungal infection in 11.9% and parasitic infection in 7.1% of the febrile episodes. Gram-negative bacteria were more frequently isolated (22/34) than Gram-positive bacteria (12/34). Staph aureus was the commonest Gram-positive organism. Kl pneumoniae and Esch coli were the common Gram-negative pathogens. The commonest organisms were sensitive to cephalosporin and gentamicin. Incidence of fever due to infection was significantly higher (p < 0.001) in patients with absolute neutropenia, in whom the mortality rate was significantly higher (p < 0.001).

Bacterial Infections↗
PubMed1994

Refolding of denatured restriction endonucleases with ribosomal preparations from Methanosarcina barkeri.

Two restriction endonucleases, EcoRI and HindIII were denatured by guanidine HC1 or by storing at room temperature denatured by guanidine HC1 or by storing at room temperature (28 degrees C) for several days. The activity of these enzymes could be restored by incubating with ribosomal preparations from an archaebacterium Methanosarcina barkeri. These results hint at a possible role of ribosomal preparations in folding polypeptides and could be useful in working with restriction enzymes in experiments on genetic engineering and molecular biology.

Bacterial Proteins↗
PubMed1993

Three flavone glycosides from Gelonium multiflorum.

Two new flavone diglycosides along with 7,4'-O-dimethylscuttelarein 6-O-beta-D-glucopyranoside, a known glycoside, were isolated from the seeds of Gelonium multiflorum and their structures were elucidated as 7,4'-O-dimethylscuttelarein 6-O-alpha-L-rhamnopyranosyl(1-->2)-beta-D-glucopyranoside and 6-O-beta-D-xylopyranosyl(1-->2)-beta-D-glucopyranoside.

Carbohydrate Sequence↗
PubMed1993

Evaluation of an on-the-job operator training method.

An experimental investigation was conducted to determine if the operators trained by the comprehensive on-the-job operator training method can maintain the production output level on a continuous basis in a repetitive production task. The components of the training method included: Methods-Time-Measurement (MTM) analysis, operator instruction sheet, demonstration, practice session, feedback, and guidance. The operators were able to sustain the production quantity and quality output levels achieved at the end of the training period for the entire experimental work session. The use of the training method is recommended.

Analysis of Variance↗
PubMed1992

Regulation of carboxypeptidase E. Effect of pH, temperature and Co2+ on kinetic parameters of substrate hydrolysis.

Carboxypeptidase E is a member of the carboxypeptidase A and B gene family, with many of the putative active-site and substrate-binding residues conserved between these enzymes. However, the pH optimum of carboxypeptidase E is substantially lower than that of carboxypeptidases A and B. To evaluate whether the difference in the pH optima of these carboxypeptidases reflects fundamental differences in the ionization behaviour of active-site residues, the influence of pH on carboxypeptidase E activity was examined. The V(max) for hydrolysis of dansyl-Phe-Ala-Arg is pH-independent between 5 and 7, but decreases at pH values below 5. The pKa for the group the protonation of which leads to the loss of activity is approximately 4.8, and the slope of the V(max.)/pH profile suggests that only a single ionizable group is involved. In contrast, Km and V(max.)/Km are dramatically influenced by pH over the range 5-7, with multiple ionizable groups detected in this pH range. The pKa of the group the protonation of which decreases the V(max.) of substrate hydrolysis is lower (4.5) for carboxypeptidase E which had been reconstituted with Co2+. The enthalpy of ionization of the group observed in the V(max.) profile for carboxypeptidase E is approx. 28.9 kJ/mol. These results are compatible with the active-site model of the homologous carboxypeptidase A: in this model the ionization of a metal-bound water molecule is responsible for the observed decrease in V(max.).

Amino Acid Sequence↗
PubMed1992

Reactivation of denatured fungal glucose 6-phosphate dehydrogenase and E. coli alkaline phosphatase with E. coli ribosome.

Fungal glucose 6-phosphate dehydrogenase and E. coli alkaline phosphatase were denatured either by physical or by chemical means. In vitro reconstitution of these denatured enzymes was assisted by 70S E. coli ribosome, as shown by the recovery of their catalytic competence. Almost total recovery of the activities of completely inactivated enzymes was obtained when 70S ribosome was present at about equimolar concentration with the enzyme molecules at 37C and 50C, respectively.

Alkaline Phosphatase↗
PubMed1992

Ganglionic nicotinic receptor agonists exhibit anti-muscarinic effects in guinea-pig olfactory cortical brain slices.

The action of some nicotinic acetylcholine receptor agonists was re-examined on the surface field potentials (N-waves) evoked by electrical stimulation of the lateral olfactory tract in guinea-pig olfactory cortical brain slices. Bath superfusion of nicotine or the nicotinic stimulants dimethylphenylpiperazinium (DMPP), lobeline, cytisine, tetramethylammonium or suberyldicholine (up to 100 microM) had little or no effect on the extracellular N-wave amplitude, or the membrane potential, input resistance or excitability of olfactory neurones recorded intracellularly. In contrast, the muscarinic agonists, carbachol or oxotremorine-M consistently depressed the field in a reversible dose-dependent manner. Interestingly, in the presence of the ganglionic stimulants DMPP (n = 6 slices) or lobeline (n = 5 slices) (10-50 microM), the effects of carbachol or oxotremorine-M were antagonized in a weak competitive-type manner (pA2 values = 5.58 and 5.63 respectively, estimated from Schild plots, constrained to unity slope). This anti-muscarinic action was unaffected by d-tubocurarine or hexamethonium. Nicotine, cytisine, tetramethylammonium and suberyldicholine showed much weaker and inconsistent carbachol-blocking effects. Combination of DMPP with atropine produced dose ratio shifts close to those predicted for a common-site interaction of two competitive antagonists. In conclusion, consistent pre- or postsynaptic nicotinic agonist actions could not be detected in olfactory cortex slices; however, some ganglionic nicotinic agonists were shown to exhibit significant anti-muscarinic effects on this preparation. We suggest this action might be due to a direct atropine-like mechanism.

Alkaloids↗
PubMed1992

Regulation of carboxypeptidase E by membrane depolarization in PC12 pheochromocytoma cells: comparison with mRNAs encoding other peptide- and catecholamine-biosynthetic enzymes.

PC12 cells, a rat pheochromocytoma cell line, have been found to express carboxypeptidase E (CPE) enzymatic activity and CPE, furin, and peptidylglycine alpha-amidating monooxygenase (PAM) mRNAs. PC12 cells secrete CPE activity in response to depolarization induced by 50 mM KCl. Short-term (1- to 3-h) treatments of PC12 cells with KCl stimulates the secretion of CPE but does not appear to stimulate the synthesis of new CPE protein, based on the measurement of CPE activity and incorporation of [35S]-Met into CPE. Also, CPE mRNA is not altered by 2-h treatments with KCl. In contrast, prolonged treatment (24-48 h) of PC12 cells with 50 mM KCl continues to stimulate the secretion of CPE activity, without altering the cellular level of CPE. Levels of CPE mRNA are significantly elevated after long-term treatment of the cells with KCl, with increases of 35% after 5 h and 55-75% after 24 to 72 h of treatment. The level of PAM mRNA is also elevated approximately 70% after 24 h of stimulation with KCl. In contrast, the mRNA levels of furin and dopamine beta-hydroxylase (DBH) do not change on treatment of PC12 cells with KCl. These findings indicate that long-term depolarization, which leads to a prolonged stimulation of PC12 cells to secrete CPE, also stimulates the synthesis of CPE and PAM but not furin or DBH.

Animals↗
PubMed1992

Secretion of carboxypeptidase E from cultured astrocytes and from AtT-20 cells, a neuroendocrine cell line: implications for neuropeptide biosynthesis.

Cultured astrocytes have recently been shown to produce certain neuropeptides, as well as neuropeptide processing enzymes. To characterize the secretory pathway in cultured astrocytes, we used the neuropeptide processing enzyme carboxypeptidase E (CPE) as a marker for neuropeptide secretion. Cultured astrocytes and AtT-20 cells, a mouse pituitary-derived neuroendocrine cell line, were labeled with [35S]Met for 15 min and then chased with unlabeled Met. CPE was isolated from either medium or cell extracts using a substrate affinity column. The time course of secretion of radiolabeled CPE was significantly different for cultured astrocytes as compared with AtT-20 cells. CPE was rapidly secreted from the astrocytes after a 30-min lag time, presumably reflecting transport through the endoplasmic reticulum and Golgi apparatus, followed by constitutive secretion. The secretion of radiolabeled CPE was essentially complete by 2 h. In contrast, only a portion of the radiolabeled CPE was secreted from AtT-20 cells over a 2-3-h period, indicating that the majority of newly synthesized CPE is stored, presumably in secretory granules within the AtT-20 cells. The regulation of CPE secretion from astrocytes was also examined. CPE secretion is stimulated two- to threefold by prolonged treatment (3-48 h) with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) but not by treatment with other secretagogues that stimulate CPE secretion from AtT-20 cells (forskolin, isoproterenol, A23187, and vasoactive intestinal peptide) or short (less than 3 h) exposure to TPA. Taken together, these results indicate that the secretory pathway for CPE, and presumably neuropeptides, is substantially different in astrocytes than the secretory pathway for CPE in neuroendocrine cells.

Animals↗